Polio once affected hundreds of thousands of people, but infections were down from around 350,000 in 1988 to fewer than 1,500 last year after a global push to vaccinate children.

While many of those infected with polio completely recover, in some it spreads to the spinal cord or brain leading to partial or complete paralysis. It is a disease that disables more often than it kills. Globally, around 10 million people are estimated to live with the effects.

There are now just four countries where polio continues to be endemic: Afghanistan, Pakistan, India and Nigeria.

"As long as it's in those four countries, it will get out and we'll have outbreaks," Gates said during his televised speech at Davos. "We had one in Tajikistan in the beginning of the year. We had one in Congo that started in the second half of the year. So we need to take these next few years and intensify the campaign"

The World Health Organization hopes to eradicate polio in two of those countries this year, ahead of its final push against the disease in 2012.

But dangers remain. Angola thought it had gotten rid of the disease, but it came back last year. A Unicef campaign to vaccinate children there recently started.

Gates was joined on stage by British Prime Minister David Cameron, who pledged to increase the UK's matching grant to &#163;40 million (US$64 million) a year for the next two years. The U.K. will provide &#163;1 for every &#163;5 donated

"I passionately believe that we have a once-in-a-lifetime opportunity to rid the world of the evil of polio," said Cameron. "We have the vaccines and the tools to do it. All that's missing is real and sustained political will to see this effort through to the end."

In addition to his foundation's monetary pledge, Gates also appears in a new campaign for Rotary International. Rotary members have raised more than a billion dollars to fight polio.

Gates' money is part of a decade-long $10 billion commitment made by the Bill and Melinda Gates Foundation to vaccination programs.

The donation, along with the work of the United Nations and international aid groups, will accomplish a lot, but Gates warns it won't be enough unless more people get on board.